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(#) Activity registered more than once

!!! ERROR: Activity registered more than once
   This is an error, and is also enforced at build time when
   supported by the build system. For Android this means it will
   run during release builds.

Id
:   `DuplicateActivity`
Summary
:   Activity registered more than once
Severity
:   Fatal
Category
:   Correctness
Platform
:   Android
Vendor
:   Android Open Source Project
Feedback
:   https://issuetracker.google.com/issues/new?component=192708
Since
:   Initial
Affects
:   Manifest files
Editing
:   This check runs on the fly in the IDE editor
Implementation
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/ManifestDetector.kt)
Tests
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/ManifestDetectorTest.kt)
Copyright Year
:   2011

An activity should only be registered once in the manifest. If it is
accidentally registered more than once, then subtle errors can occur,
since attribute declarations from the two elements are not merged, so
you may accidentally remove previous declarations.

(##) Example

Here is an example of lint warnings produced by this check:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text
AndroidManifest.xml:15:Error: Duplicate registration for activity
com.example.helloworld.HelloWorld [DuplicateActivity]
    &lt;activity android:name="com.example.helloworld.HelloWorld"
              ------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here are the relevant source files:

`AndroidManifest.xml`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~xml linenumbers
&lt;manifest xmlns:android="http://schemas.android.com/apk/res/android"
     package="com.example.helloworld"
     android:versionCode="1"
     android:versionName="1.0"&gt;
   &lt;uses-sdk android:minSdkVersion="14" /&gt;
   &lt;application android:icon="@drawable/icon" android:label="@string/app_name"&gt;
       &lt;activity android:name=".HelloWorld"
                 android:label="@string/app_name"&gt;
           &lt;intent-filter&gt;
               &lt;action android:name="android.intent.action.MAIN" /&gt;
               &lt;category android:name="android.intent.category.LAUNCHER" /&gt;
           &lt;/intent-filter&gt;
       &lt;/activity&gt;

       &lt;activity android:name="com.example.helloworld.HelloWorld"
                 android:label="@string/app_name"&gt;
       &lt;/activity&gt;

   &lt;/application&gt;

&lt;/manifest&gt;
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

`res/values/strings.xml`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~xml linenumbers
&lt;!-- Copyright (C) 2007 The Android Open Source Project

     Licensed under the Apache License, Version 2.0 (the "License");
     you may not use this file except in compliance with the License.
     You may obtain a copy of the License at

          http://www.apache.org/licenses/LICENSE-2.0

     Unless required by applicable law or agreed to in writing, software
     distributed under the License is distributed on an "AS IS" BASIS,
     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     See the License for the specific language governing permissions and
     limitations under the License.
--&gt;

&lt;resources&gt;
    &lt;!-- Home --&gt;
    &lt;string name="home_title"&gt;Home Sample&lt;/string&gt;
    &lt;string name="show_all_apps"&gt;All&lt;/string&gt;

    &lt;!-- Home Menus --&gt;
    &lt;string name="menu_wallpaper"&gt;Wallpaper&lt;/string&gt;
    &lt;string name="menu_search"&gt;Search&lt;/string&gt;
    &lt;string name="menu_settings"&gt;Settings&lt;/string&gt;
    &lt;string name="sample" translatable="false"&gt;Ignore Me&lt;/string&gt;

    &lt;!-- Wallpaper --&gt;
    &lt;string name="wallpaper_instructions"&gt;Tap picture to set portrait wallpaper&lt;/string&gt;
&lt;/resources&gt;

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can also visit the
[source code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/ManifestDetectorTest.kt)
for the unit tests for this check to see additional scenarios.

The above example was automatically extracted from the first unit test
found for this lint check, `ManifestDetector.testDuplicateActivity`.
To report a problem with this extracted sample, visit
https://issuetracker.google.com/issues/new?component=192708.

(##) Suppressing

You can suppress false positives using one of the following mechanisms:

* Adding the suppression attribute `tools:ignore="DuplicateActivity"`
  on the problematic XML element (or one of its enclosing elements).
  You may also need to add the following namespace declaration on the
  root element in the XML file if it's not already there:
  `xmlns:tools="http://schemas.android.com/tools"`.

  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;manifest xmlns:tools="http://schemas.android.com/tools"&gt;
      ...
      &lt;application tools:ignore="DuplicateActivity" .../&gt;
    ...
  &lt;/manifest&gt;
  ```

* Using a special `lint.xml` file in the source tree which turns off
  the check in that folder and any sub folder. A simple file might look
  like this:
  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;lint&gt;
      &lt;issue id="DuplicateActivity" severity="ignore" /&gt;
  &lt;/lint&gt;
  ```
  Instead of `ignore` you can also change the severity here, for
  example from `error` to `warning`. You can find additional
  documentation on how to filter issues by path, regular expression and
  so on
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html).

* In Gradle projects, using the DSL syntax to configure lint. For
  example, you can use something like
  ```gradle
  lintOptions {
      disable 'DuplicateActivity'
  }
  ```
  In Android projects this should be nested inside an `android { }`
  block.

* For manual invocations of `lint`, using the `--ignore` flag:
  ```
  $ lint --ignore DuplicateActivity ...`
  ```

* Last, but not least, using baselines, as discussed
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).

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